This project seeks to answer the question whether the standard practice of hemodilution during Cardiopulmonary Bypass Surgery contributes to neurocognitive dysfunction postoperatively. This study will enroll 370 subjects over four years with the primary outcome measure consisting of a battery of neurocognitive tests administered preoperatively and at two time points after surgery. Follow-up testing is done at 6 weeks after surgery and one year after surgery. Subjects recruited to group one will receive less hemodilution (HCT values 27% and above) Subjects randomized to group two will receive customary hemodilution. (HCT values between 15% to 18%.)